Billionaire Mike Bloomberg must be grilled by lawyers in a legal fight with several ex-employees, a Manhattan judge has ruled.

Federal Judge Richard Casey ordered the mayor-elect to sit for a deposition in a lawsuit Bloomberg filed over billing practices at his company’s offices in Princeton, N.J.

Bloomberg sued ex-employee Joseph Menno and several others in 1999 charging they conspired to rip off his company by padding bills and then laundering kickbacks to each other.

The mogul accused Menno of setting up a contracting company with his brother, John, which ostensibly provided services to Bloomberg, but which he alleged was really created to overcharge Bloomberg’s financial news empire.

One 1995 bill for $944 in cable-installation work was jacked up to $11,760, the suit claims.

Bloomberg’s lawyers are seeking more than $12 million in damages in the case, and say the company learned of the chicanery in 1997 during a routine internal audit.

One person charged in the lawsuit, William Kramer, pleaded guilty in 1998 to criminal conspiracy and mail fraud.

Bloomberg had agreed to the deposition in July, but defense lawyers in the case went back to the judge this month to complain the mogul was stalling.

Casey signed papers just before Christmas telling Bloomberg to sit for the deposition.

A lawyer for one of the men being sued by Bloomberg did not return a call for comment.

Sources close to Bloomberg’s legal team say he will not try to dodge the Q&A session even though he’s about to start work at City Hall.